JP2757896B2 - Photovoltaic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device, and more particularly to a photovoltaic device used as a solar cell having high initial photoelectric conversion efficiency, low photodegradation and high stability over a long period of time.

[0002]

2. Description of the Related Art
In various devices, a solar cell is used as a driving energy source. In particular, amorphous silicon solar cells have been steadily spreading as power supplies for consumer devices such as calculators, watches, and radios.

[0003] While these consumer solar cells are often used indoors, power solar cells use rain, wind,
It is mainly installed outdoors where light and temperature change are severe. For this reason, it is necessary for a power solar cell to withstand severe natural environment and to continue generating power for a long period of time, and the level of performance and price is more demanding than that of consumer use.

[0004] Therefore, in order to commercialize the amorphous silicon solar cell for electric power, it is necessary to develop a few advanced technologies for consumer use.

[0005] Among these demands for performance improvement, in particular, stacked solar cells having different optical band gaps have been developed so as to more efficiently collect each part of the spectrum of the solar ray in order to improve the photoelectric conversion efficiency. Proposed.

For example, as disclosed in US Pat. No. 4,253,882, a stacked solar cell in which an amorphous semiconductor is stacked in a first cell on the light incident side and a crystalline semiconductor is stacked in a second cell, U.S. Pat.No. 4,377,723, Japanese Patent Publication No.
There is an amorphous semiconductor laminated solar cell made of a heterogeneous material as disclosed in the specification of JP-A-62-26196. In any of these, the optical band gap of the first cell on the light incident side is larger than the optical band gap of the second cell, and light passing through the first cell is efficiently absorbed by the second cell. A stacked solar cell having such a configuration is intended to improve the photoelectric conversion efficiency.

[0007] However, none of these technologies is sufficient in terms of long-term stability under the use environment, particularly low light deterioration.

[0008] In the stacked solar cell having the same layer structure as the above-described stacked solar cell, a low-light-deteriorated solar cell having long-term stability, for example, "New Energy and Industrial Technology Development Organization" , Annual Report of Research Results [II]
, 9110, 1988, and the like, it has been proposed to make the photoactive region of each cell thinner.

However, in consideration of the initial photoelectric conversion efficiency, there is a limit to the thinning of the photoactive region of each cell, and it has not been a satisfactory technology in terms of sufficient photoelectric conversion efficiency and long-term stability.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a photovoltaic device which has the above-mentioned problems of the prior art, that is, a photovoltaic device having high photoelectric conversion efficiency and excellent long-term stability under the use environment. .

[0011]

To achieve the above object, according to an aspect of the present invention, in the plurality having photovoltaic device stacked photovoltaic cell includes a semi-conductor layer of the photoactive light incident side
Optical band gap of the semiconductor layer of the first optical activity of the photovoltaic cells of upper, lower portion of the first photovoltaic cell
Second the rather smaller than the optical band gap of the semiconductor layer of the optical activity of the photovoltaic cell, wherein the first photovoltaic cell
The thickness of the photoactive semiconductor layer of the second photovoltaic cell is
An object of the present invention is to provide a photovoltaic device characterized by being thinner than the thickness of the photoactive semiconductor layer .

The optically active semiconductor layer used in the first photovoltaic cell has an optical band gap of 1.44.
1.52 eV, the film thickness is 200-450 °,
The above problem is caused by the photovoltaic device, wherein the photoactive semiconductor layer used in the second photovoltaic cell has an optical band gap of 1.70 to 1.75 eV and a thickness of 3000 to 6000 °. May be resolved.

The optically active semiconductor layer used in the first photovoltaic cell has an optical band gap of 1.44.
1.52 eV, the film thickness is 350-650 °,
According to a photovoltaic device, the photoactive semiconductor layer used in the second photovoltaic cell has an optical band gap of 1.60 to 1.67 eV and a thickness of 1500 to 4500 °. May be resolved. The light
The active semiconductor layer is an i-type semiconductor layer.
It is also a photovoltaic device.

[0014]

According to the above-mentioned means of the present invention, in a photovoltaic device in which at least two photovoltaic cells are stacked, the optical band gap of the photoactive region of the first cell on the light incident side is reduced to the second. When the optical band gap is smaller than the optical band gap of the photoactive region of the second cell, the photoactive region of the first cell can be made extremely thin. For this reason,
It is considered that since the internal electric field that causes the charge carriers generated inside by the irradiation light to drift becomes stronger, the photodegradation effect due to the residual load carriers is reduced, and a photovoltaic device with low photodegradation can be produced.

[Embodiment] An example of the layer structure of the photovoltaic device of the present invention will be described below, but the photovoltaic device of the present invention is not limited thereto.

FIGS. 1A and 1B are cross-sectional views schematically showing a typical example of a layer structure as a photovoltaic device of the present invention.

FIG. 1A shows an example in which a lower electrode 102, an n-type semiconductor layer 103, and an i-type semiconductor layer 1 are formed on a support 101.
04, p-type semiconductor layer 105, n-type semiconductor layer 106, i-type semiconductor layer 107, p-type semiconductor layer 108, transparent electrode 10
9 and a photovoltaic device 120 in which current collecting electrodes 110 are sequentially formed. In addition, in the photovoltaic device of this example, light 130 is incident from the transparent electrode 109 side. The light incident side pin junction photovoltaic cell 111 is defined as a first cell, and the pin junction type photovoltaic cell 112 not on the light incidence side is defined as a second cell.

FIG. 1B shows an example of a light-transmitting support 10.
1, a transparent electrode 109, a p-type semiconductor layer 108, an i-type semiconductor layer 107, an n-type semiconductor layer 106, and a p-type semiconductor layer 10
5, a photovoltaic device 120 in which an i-type semiconductor layer 104, an n-type semiconductor layer 103, and a lower electrode 102 are formed in this order.
It is. In this photovoltaic device, it is assumed that light is incident from the transparent support 101 side. The light incident side pin junction type photovoltaic cell 111 is used as the first cell, and the pin junction type photovoltaic cell 112 not on the light incident side is used.
Is the second cell.

Hereinafter, such a configuration in the present invention will be specifically described step by step for each component.

(Support) The support 101 used in the present invention may be a single crystalline or non-single crystalline substrate.
Further, it may be electrically insulating. Furthermore, they may be translucent or non-translucent, but when light is incident from the support 101 side, they are translucent. It is necessary.

As specific examples thereof, Fe, Ni, Cr, Al, Mo, A
Examples thereof include metals such as u, Nb, Ta, V, Ti, Pt, and Pb, and alloys thereof, for example, brass, stainless steel, and the like.

In addition to these, there may be mentioned films or sheets of synthetic resins such as polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide and polyimide, glass, ceramics and the like.

Further, as a single crystalline support, Si, Ge, C, Na
Cl, KCl, LiF, GaSb, InAs, InSb, GaP, MgO, CaF 2, BaF 2, α-
Examples thereof include those sliced from a single crystal such as Al ₂ O ₃ and processed into a wafer shape, and those obtained by epitaxially growing the same material or a material having a similar lattice constant on these.

The shape of the support may be plate-like, long belt-like, cylindrical or the like having a smooth surface or an uneven surface depending on the purpose and application. The thickness of the support is as desired. Is determined as appropriate so that the photovoltaic device is required to be flexible, or when light is incident from the side of the support, the function as the support is sufficiently exhibited. It can be as thin as possible within the range. However, the thickness is usually 10 μm from the viewpoint of production and handling of the support, mechanical strength and the like.

(Electrode) In the photovoltaic device of the present invention, an appropriate electrode is selectively used depending on the configuration of the device. Examples of these electrodes include a lower electrode, an upper electrode transparent electrode, and a current collecting electrode. (However, the upper electrode referred to here is the one provided on the light incident side,
The lower electrode means an electrode provided to face the upper electrode with a semiconductor layer interposed therebetween. ) These electrodes are described in detail below.

(I) Lower Electrode As the lower electrode 102 used in the present invention, a surface to which light for generating photovoltaic power is irradiated depends on whether the material of the support 101 is translucent or not. (For example, when the support 101 is a non-translucent material such as a metal, light for photovoltaic generation is irradiated from the transparent electrode 109 side as shown in FIG. 1A). , The place where it is installed is different.

More specifically, in the case of a layer structure as shown in FIG. 1A, it is provided between the support 101 and the n-type semiconductor layer 103. However, when the support 101 is conductive, the support can also serve as the lower electrode. However, if the sheet resistance is high even if the support 101 is conductive, the electrode is used as a low-resistance electrode for extracting current or for the purpose of increasing the reflectivity on the support surface and making effective use of incident light. 102 may be installed.

In the case of FIG. 1B, the light-transmitting support 10
1 is used, and light enters from the side of the support 101, so that the lower electrode 102 faces the support 101 and sandwiches the semiconductor layer for the purpose of current extraction and light reflection at the electrode. It is provided in.

When an electrically insulating material is used as the support 101, the lower electrode 10 is provided between the support 101 and the n-type semiconductor layer 103 as a current extracting electrode.
2 are provided.

As electrode materials, Ag, Au, Pt, Ni, Cr, Cu, A
l, Ti, Zn, Mo, W and other metals, or alloys thereof, and thin films of these metals are deposited by vacuum evaporation, electron beam evaporation,
It is formed by sputtering or the like. Also, the formed metal thin film must be considered so as not to become a resistance component with respect to the output of the photovoltaic device, and therefore, as a sheet resistance value,
Preferably, it is 50Ω or less, more preferably 10Ω or less.

Although not shown in the figure, a diffusion preventing layer such as conductive zinc oxide may be provided between the lower electrode 102 and the n-type semiconductor layer 103. The effect of the diffusion prevention layer is not only to prevent the metal element forming the electrode 102 from diffusing into the n-type semiconductor layer, but also to provide a small resistance value so that the lower portion provided between the semiconductor layers is provided. The effect of preventing short-circuiting caused by a defect such as a pinhole between the electrode 102 and the transparent electrode 106 and generating multiple interference by a thin film to confine incident light in a photovoltaic element are given. be able to.

(Ii) Upper Electrode (Transparent Electrode) As the transparent electrode 109 used in the present invention, in order to efficiently absorb light from the sun or a white fluorescent lamp into the semiconductor layer,
The light transmittance is desirably 85% or more, and more preferably, the sheet resistance is desirably 100Ω or less so that the output of the photovoltaic element does not become a resistance component. Materials having such properties include SnO ₂ , In ₂ O
Metal oxides such as ₃ , ZnO, CdO, Cd ₂ SnO ₄ , ITO (In ₂ O ₃ + SnO ₂ ), and metal thin films such as Au, Al, Cu etc. No. The transparent electrode is laminated on the p-type semiconductor layer 108 in FIG.
In (B), since they are stacked on the substrate 101, it is necessary to select ones having good adhesion to each other. In addition, as a manufacturing method of these, resistance heating evaporation method,
An electron beam heating vapor deposition method, a sputtering method, a spray method, or the like can be used, and is appropriately selected as desired.

(Iii) Current-collecting electrode The current-collecting electrode 110 used in the present invention is a transparent electrode 109 for the purpose of reducing the surface resistance of the transparent electrode 109.
Provided above. Ag, Cr, Ni, Al, Ag, Au,
Thin films of metals such as Ti, Pt, Cu, Mo, W or alloys thereof. These thin films can be stacked and used. The shape and area of the semiconductor layer are appropriately designed so that the amount of light incident on the semiconductor layer is sufficiently ensured.

For example, it is desirable that the shape is uniformly spread over the light receiving surface of the photovoltaic device, and the area is preferably 15% or less, more preferably 10% or less with respect to the light receiving area. .

The sheet resistance is preferably 5
It is desirable that the resistance is 0Ω or less, more preferably 10Ω or less.

(I-Type Semiconductor Layer) The i-type semiconductor layer is a photoactive semiconductor layer in the present invention.
Function. The semiconductor material constituting the i-type semiconductor layer suitably used in the present invention includes A-Si: H, A-Si: F,
Si: H: F, A-SiC: H, A-SiC: F, A-SiC: H: F, A-SiGe: H, A-SiGe:
F, A-SiGe: H: F, poly-Si: H, poly-Si: F, poly-Si: H: F and the like.

The i-type semiconductor layer suitably used in the present invention is used in the case where the i-type semiconductor layer is used for the first cell 111 on the light incident side and in the case where the i-type semiconductor layer is used for the second cell 112 which is not on the light incident side. It is appropriately determined in some cases. Further, as shown in the evaluation results of Examples described later, the following two combinations of 1) and 2) are available as combinations of the optical band gap and the film thickness of the i-type semiconductor layer in which the effects of the present invention can be obtained. Conceivable.

1) The optical band gap of the i-type semiconductor layer 107 used in the first cell 111 on the light incident side is 1.44 to 1.44.
1.52 eV, and the film thickness is preferably 200 ° -45 °
0 ° and optimally between 250 ° and 400 °.

The optical band gap of the i-type semiconductor layer 104 used for the second cell 112 not on the light incident side is
1.70 to 1.75 eV, and the film thickness is preferably 3000
Å-6000Å, optimally 3500Å-5500
Å.

Hereinafter, the reason will be described.

When the thickness of the i-type semiconductor layer 107 used for the first cell 111 is less than 200 °, the output current of the solar cell is reduced because the semiconductor layer is thin, and the photoelectric conversion efficiency is significantly reduced. When the thickness of the semiconductor layer exceeds 450 °, the thickness of the semiconductor layer is large, so that the amount of light transmitted to the second cell 112 decreases, and the output current of the solar cell in the second cell decreases. There is a disadvantage that the photoelectric conversion efficiency is significantly reduced.

When the thickness of the i-type semiconductor layer 104 used in the second cell 112 is less than 3000 °, the output current of the solar cell decreases because the semiconductor layer is thin, and the photoelectric conversion efficiency decreases. When the thickness of the semiconductor layer exceeds 6000 °, the semiconductor layer is too thick, so that the fill factor (Fi11-Factor) of the solar cell is reduced and the photoelectric conversion efficiency is reduced. Occurs.

2) The optical band gap of the i-type semiconductor layer 107 used in the first cell 111 on the light incident side is 1.44 to 1.44.
1.52 eV, and its film thickness is preferably 350 ° -65 ° C.
0 °, optimally between 400 ° and 600 °.

The optical band gap of the i-type semiconductor layer 104 used in the second cell 112 not on the light incident side is
1.60 ~ 1.67eV, its film thickness is preferably 1500 ~ 4
500 °, optimally between 2000 ° and 4000 °.

Hereinafter, the reason will be described.

When the thickness of the i-type semiconductor layer 107 used for the first cell 111 is less than 350 °, the output current of the solar cell is reduced due to the thin semiconductor layer, and the photoelectric conversion efficiency is significantly reduced. When the thickness of the semiconductor layer exceeds 650 °, the thickness of the semiconductor layer increases.
The amount of light transmitted through the second cell 112 is reduced, the output current of the solar cell in the second cell is reduced, and the photoelectric conversion efficiency is significantly reduced.

When the thickness of the i-type semiconductor layer 104 used in the second cell 112 is less than 1500 °, the output current of the solar cell decreases due to the thin semiconductor layer, and the photoelectric conversion efficiency decreases. When the thickness of the semiconductor layer exceeds 4500 °, the fill factor (Fi11-Factor) of the solar cell is reduced due to the thick semiconductor layer, and the photoelectric conversion efficiency is reduced. Disadvantages arise.

Note that the optical band gap of the i-type semiconductor layer has a light absorption spectrum as shown in FIG.

[0049]

(Equation 1)  Is plotted as₀ Was obtained.

(Method of Forming i-Type Semiconductor Layer) A deposition film forming apparatus and a deposition film forming method suitable for forming an i-type semiconductor layer of the present invention will be described.

In this method, Si source gas, Ge
A source gas such as a system-based source gas, a C-based source gas, an H ₂ gas, or an F ₂ gas is introduced, and a high-frequency power is applied to a cathode electrode installed in the film formation chamber, and plasma generated by glow discharge is formed in the film formation chamber. Is formed, and an i-type semiconductor layer is formed on the substrate heated and held in the film formation chamber.

The energy source used to decompose the raw material gas is not limited to high frequency power, but may be microwave energy, heat energy, or light energy.

Further, as the Si-based source gas, SiH ₄ , Si
_{2 H 6, Si 3 H 8} , SiF 4, Si -based gas such as Si ₂ F ₆ can be used.

As the Ge source gas, GeH ₄ , Ge
F ₄ , Ge ₂ H ₆ , Ge ₂ F _{2 and the} like can be used.

As the C-based source gas, CH ₄ , C ₂ H
_{6, C 3 H 8, C} 2 H 4, C 2 H 2, C 3 H 6, C 6 H 6, CF 4 or the like can be used.

A detailed description will be made specifically with reference to a schematic diagram of the deposited film forming apparatus shown in FIG.

First, in FIG. 2, reference numeral 201 denotes a film forming chamber having means for carrying out the method of the present invention, wherein a substrate 203 is held on a substrate holding cassette 202 and a substrate transport jig 2 is provided.
06 can be moved. Reference numeral 204 denotes a thermocouple, which is used for monitoring when the temperature of the substrate 203 is heated and held by the heater 205. Reference numeral 213 denotes a load lock chamber, which has a built-in substrate transfer jig 206 and can vacuum transfer the substrate via a gate valve 207.

Reference numeral 216 denotes a film formation chamber which is effectively used when a semiconductor layer made of a material different from that formed in the film formation chamber 201 is laminated. A similar or other different film forming means is provided (not shown).

Reference numeral 212 denotes a cathode electrode, which is supplied with high-frequency power from a high-frequency power supply 210 via a matching box 211, and converts source gases introduced from the gas introduction pipes 208 and 209 into plasma. Various radicals, various ions, and the like generated in the plasma reach the substrate 203 while causing a chemical interaction, and an i-type semiconductor layer having desired characteristics is formed. An exhaust pump 215 controls the pressure in the film forming chamber 201 monitored by the pressure gauge 217 by adjusting the opening of the throttle valve 214.

Hereinafter, the results of experiments conducted by the present inventors will be described in detail with reference to FIG.

[Experiment 1] 2 inches × 2 inches, thickness 0.8 m
The # 7059 glass substrate 203 manufactured by Corning Corporation was set on the substrate holding cassette 202, and a-SiGe: H film samples No. 1 to 8 were formed under the film forming conditions shown in Table 1.

As a source gas, Si ₂ H ₆ gas and H ₂ gas are introduced into the film forming chamber 201 through a gas introduction pipe 208 from a cylinder (not shown), and GeH ₄ gas is supplied from the cylinder (not shown) as a source gas. Was introduced into the film forming chamber 201 through the introduction pipe 209.

The optical band gap of the obtained sample was determined by the method described above. Also, Cr
A comb-shaped electrode (gap length 250 μm, length 5 cm) was deposited, and the electrical conductivity was determined using a 5 mW He-Ne laser.

From these results, it was found that a deposited film having desired characteristics (optical band gap) can be formed by changing the flow rate of the introduced GeH ₄ gas.

[0065]

[Table 1] [Experiment 2] A # 7059 glass substrate 203 manufactured by Corning and having a size of 2 inches x 2 inches and a thickness of 0.8 mm was set on a substrate holding cassette 202, and a-Si: H film sample No. 11 was formed under the film forming conditions shown in Table 2. ~ 16 were produced.

As a source gas, a Si ₂ H ₆ gas was introduced from a cylinder (not shown) into the film forming chamber 201 through a gas introduction pipe 208.

For the obtained sample, the optical energy band gap E _g opt and the photoconductivity were determined in the same manner as in [Experiment 1].

From these results, it was found that a semiconductor layer having a desired optical band gap can be formed by changing the substrate temperature.

[0069]

[Table 2] (Method of forming n-type and p-type semiconductor layers) (1) n-type semiconductor layer Using a forming apparatus similar to the i-type semiconductor layer forming apparatus,
PH ₃ / as a source gas containing P which is a valence electron controlling atom
Films were formed under the following conditions using 1% of H ₂ , and the results are shown in Table 3.

[0070]

[Table 3] In addition, PF ₅ , PCl ₃ , PF ₃ or the like may be used as the raw material gas in addition to PH ₃ . (2) p-type semiconductor layer p-type semiconductor layer
BF ₃ /
Using H ₂ 2%, a film was formed under the following conditions, and the results are shown in Table 4.

[0071]

[Table 4] Note Besides BF ₃ as a source _{gas, B 2 H 6, BCl 3} , BBr 3 , etc. may be used. (Method of forming pin junction)
As a means for forming an in-junction, it is desirable that the formation of the n-type semiconductor layer, the formation of the i-type semiconductor layer, and the formation of the p-type semiconductor layer be performed continuously in a vacuum. Specifically, in the case where the semiconductor layers are formed continuously in the same volume film forming apparatus, or when the respective semiconductor layers are formed using different apparatuses, the respective deposited film forming apparatuses are connected via a gate valve or the like. Then, for example, after forming an n-type semiconductor layer with the first deposited film forming apparatus, the substrate on which the n-type semiconductor layer is formed is transported to the second deposited film forming apparatus under vacuum conditions, An i-type semiconductor layer is formed by the deposited film forming apparatus, and the substrate formed up to the i-type semiconductor layer is transported to a third deposited film forming apparatus under vacuum conditions. Then, a p-type semiconductor layer may be formed, and this may be repeated to form a stacked photovoltaic device.

[0072]

EXAMPLES The stacked photovoltaic device of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(Example 1) The pin junction type stacked photovoltaic device shown in FIG. 1A was used for the above-described experimental examples 1 and 2 of the present invention by using the deposited film forming apparatus having the structure shown in FIG. The film was prepared by the following procedure according to the film forming method.

A stainless steel substrate 101 having a size of 50 mm × 50 mm is placed in a sputtering apparatus (not shown), and
After evacuating to a vacuum of 0 ^-5 Torr or less, an Ag thin film of about 1000 ° serving as the lower electrode 102 was deposited on the substrate 101 using Ar as a sputtering gas.

The substrate 101 is taken out, and the surface on which the lower electrode 102 has been deposited is fixed on the substrate holding cassette 202 on the substrate transfer jig 206 in the load lock chamber 213 so as to face downward in FIG. The gas is exhausted to a pressure of 10 ⁻⁵ Torr or less by an exhaust pump 215 (not shown) in the lock chamber 213. When the pressures in both chambers become almost equal, the gate valve 207 is opened, and the substrate transfer jig 206 is used to
The substrate holding cassette 202 is moved into the film forming chamber 201,
The gate valve 207 was closed again.

Next, heating was performed by the heater 205 so that the surface temperature of the substrate 203 became 350 ° C. When the substrate temperature was stabilized, 10 sccm of Si ₂ H ₆ gas and 440 sccm of H ₂ gas stored in a cylinder (not shown) were mixed and introduced into the film forming chamber 201 from the gas supply pipe 208. At the same time, PH ₃ (1% diluted with H ₂ ) stored in a cylinder (not shown) was introduced into the film forming chamber 201 from the gas supply pipe 209 at a flow rate of 50 sccm. Next, the opening degree of the exhaust valve 214 was adjusted, and while the internal pressure of the film forming chamber 201 was maintained at 1.2 Torr,
An electric power of 15 w was supplied from the high frequency power supply 210 of 13.56 MHz into the film forming chamber 201.

By the above operation, aS as an n-type semiconductor is obtained.
The i: H film 103 was formed (the above was in accordance with the film forming conditions in Table 3 which is the method for forming an n-type semiconductor layer).

After the formation of the n-type a-Si: H film at 250 °, the introduction of the gas and the supply of the high frequency power were stopped, and the inside of the film forming chamber 201 was evacuated to 10 ^-5 Torr or less by the exhaust pump 215.

Next, with the same configuration as the film forming chamber 201,
The substrate 203 formed up to the n-type semiconductor layer 103 is transferred to the substrate transfer jig 2 into the film formation chamber 216 evacuated to 10 ⁻⁵ Torr.
06 and moved.

Hereinafter, the structure inside the film forming chamber 216 will be described.
Therefore, description will be made using the same drawing numbers as those shown in FIG.

Next, heating was performed by the heater 205 so that the surface temperature of the substrate 203 deposited up to the n-type semiconductor layer was 350 ° C. When the substrate temperature is stabilized, 11 sccm of Si ₂ H ₆ gas and 5 H ₂ gas stored in a cylinder (not shown)
The mixture was introduced into the film forming chamber 201 from the gas supply pipe 208 while mixing 60 sccm.

Next, the opening of the exhaust valve 214 is adjusted.
While maintaining the internal pressure of the film forming chamber 201 at 1.15 Torr, 14 w was supplied into the film forming chamber 201 from the 13.56 MHz high frequency power supply 210.

By the above operation, as an i-type semiconductor, aS
The i: H film 104 was formed (the above was in accordance with the film forming conditions in Table 2 which is the i-type semiconductor layer forming method).

Next, after forming a 4000 ° i-type a-Si: H film,
The introduction of the gas and the supply of the high frequency power were stopped, and the inside of the film forming chamber 201 was evacuated to 10 ^-5 Torr or less by the exhaust pump 215.

Next, the substrate 203 formed up to the i-type semiconductor layer 104 is removed from the film forming chambers 201 and 216 by the same operation as described above.
It was transported to the film formation chamber 218 having the same configuration as that of FIG. Hereinafter, the film forming chamber 21
The configuration in 6 is the same as that of the film forming chamber 201 and will be described with the same drawing numbers as those shown in FIG.

Next, heating was performed by the heater 205 so that the surface temperature of the substrate 203 deposited up to the i-type semiconductor layer was 250 ° C. When the substrate temperature becomes stable, the SiH ₄ (5% diluted with H ₂ ) gas 5 stored in a cylinder (not shown)
The sccm and the H ₂ gas 355 sccm were mixed and introduced into the film formation chamber 218 from the gas supply pipe 208. At the same time, BF ₃ (2% diluted with H ₂ ) stored in a cylinder (not shown)
The gas was introduced into the film forming chamber 218 from the gas supply pipe 209 at a flow rate of sccm. Next, the opening degree of the exhaust valve 214 is adjusted,
While maintaining the internal pressure of the film forming chamber 218 at 2.0 Torr, 330 w of electric power was supplied from the 13.56 MHz high frequency power supply 210 into the film forming chamber 218.

Through the above operation, a microcrystalline silicon semiconductor 105 (of course, microcrystalline silicon falls within the range of an amorphous silicon semiconductor) was formed as a p-type semiconductor (the above is the method of forming a p-type semiconductor layer). The film forming conditions in Table 4 were followed.)

Next, after the formation of the p-type microcrystalline silicon film of 100 °, the introduction of the gas and the supply of the high frequency power were stopped, and the inside of the film forming chamber 218 was evacuated to 10 ^-5 Torr or less by the exhaust pump 215.

As described above, the second cell 112 was manufactured.

Next, the substrate on which the second cell 112 is formed is vacuum-transferred to the film forming chamber 201, and then the same operation is carried out except that the substrate temperature is set to 250 ° C. in the n-type semiconductor layer forming method. Then, a 100 ° n-type semiconductor 106 was formed.

Next, by the same operation as described above, the film forming chamber 20
After the vacuum transfer into the film forming chamber 216 as in
At 5, heating was performed so that the surface temperature of the substrate 203 deposited on the second cell 112 up to the n-type semiconductor layer was 250 ° C.

When the substrate temperature becomes stable, 12 sccm of Si ₂ H ₆ gas and 550 H ₂ gas stored in a cylinder (not shown)
While the sccm is mixed, the film forming chamber 21 is
6 was introduced. At the same time, it was stored in a cylinder (not shown)
GeH ₄ gas 4.5 sccm was supplied from the gas supply pipe 209 to the film forming chamber 2.
16 was introduced.

Next, the opening of the exhaust valve 214 is adjusted.
While maintaining the internal pressure of the film forming chamber 216 at 1.1 Torr, a power of 15 w was supplied from the 13.56 MHz high frequency power supply 210 into the film forming chamber 218.

By the above operation, a-Si is used as an i-type semiconductor.
A Ge: H film 107 was formed (the above was in accordance with the film forming conditions in Table 1 which is an i-type semiconductor layer forming method).

Next, after the formation of the i-type a-SiGe: H film at 350 ° C., the introduction of the gas and the supply of the high frequency power were stopped, and the inside of the film formation chamber 216 was evacuated by the exhaust pump 215 at 10 ^-5 Torr.

Next, the substrate 203 formed up to the i-type semiconductor layer 107 is vacuum-transferred to the film forming chamber 218 by the same operation as described above, and then the substrate temperature is set to 200 ° C. in the p-type semiconductor layer forming method. With exactly the same operation and method,
A 0 ° p-type semiconductor 108 was formed.

As described above, the first cell 111 was formed on the second cell 112.

Next, the substrate holding cassette 202 is moved by the substrate transfer jig 206 to a take-out load lock chamber (not shown) via the gate valve 207, and after cooling, the first
The substrate 203 on which the cell 111 and the second cell 112 were stacked and deposited was taken out.

The substrate 203 was placed in a vacuum deposition apparatus in which a deposition board filled with metal particles of In and Sn at a weight ratio of 1: 1 was set and evacuated to 10 ⁻⁵ Torr or less. As a result, an ITO thin film as the transparent electrode 109 was deposited in an oxygen atmosphere of about 1 × 10 ⁻³ Torr by about ⁷⁰⁰ °.
The substrate heating temperature at this time was 170 ° C.

[0100] After cooling, remove the substrate 203, placed in a vacuum evaporation apparatus in close contact permalloy mask made for current collection electrode pattern formed on the upper surface of the transparent electrode 109, 1 × 10 ^-5 To
After evacuation to rr or less, the thickness of Ag was
0.8 μm was deposited to produce a comb-like current collecting electrode 110.

By the above operation and method, the stacked photovoltaic device shown in FIG. 1A was manufactured.

In this embodiment, the first cell has the optical band gap E _g opt = 1.48 eV of the sample No. 4 shown in Table 1 and the second cell has the sample No. 15 shown in Table 2 as the second cell.
The optical band gap E _g opt was 1.70, and the optical band gap was (first cell) <(second cell).

As a comparative example, a photovoltaic device of Comparative Example 1 described below was manufactured. (Comparative Example 1) In this comparative example, each of the first cell 111 and the second cell 112 of the first embodiment,
A stacked photovoltaic device was manufactured while changing each of 07 and 104 independently.

Table 7 shows the manufacturing conditions of the stacked photovoltaic device of this comparative example. As shown in the table, in this example, as the first cell, the optical band gap E _g opt = 1.73 eV of Sample No. 14 shown in Table 2 was used, and as the second cell, the sample No. 14 shown in Table 1 was used. Optical band gap E _g opt = 1.48 eV for 4
And the optical band gap is (first cell)> (second cell).
Cell).

[0105]

[Table 5]

[0106]

[Table 6]

[0107]

[Table 7] (Results) The characteristics of the stacked photovoltaic devices of Example 1 and Comparative Example 1 described above were evaluated as follows.

AM-1.5 light (100 mW /
cm ² ), the initial photoelectric conversion efficiency of Example 1 was comparable to that of the prior art shown in Comparative Example 1.

Next, the stacked photovoltaic device of the first embodiment was
The sample was placed in an irradiation light beam of -1.5 (100 mW / cm ² ), irradiated with light for 1500 hours while maintaining an optimum load condition and an apparatus temperature of 41 ° C., and evaluated for light deterioration characteristics. When the ^* deterioration rate with respect to the initial photoelectric conversion efficiency was defined and measured as follows, the degradation rate of Example 1 was improved by about 6% as compared with the prior art shown in Comparative Example 1.

[0110]

[Equation 2] Initial photoelectric conversion efficiency-photoelectric conversion efficiency after 1500 hours * Degradation rate = ─────────────────────── x 100 Initial photoelectric conversion efficiency ( Embodiment 2) In this embodiment, each of the first cell 111 and the second cell 112 in the first embodiment, i.
A stacked photovoltaic device was manufactured while independently changing the optical band gaps of Examples and 104, and the same evaluation as in Example 1 was performed.

The evaluation results are shown in FIG. 4 (the evaluation results are shown in a relative ratio with the prior art being 1.0, as in Example 1).

In FIG. 4, for example, the point ▽ indicates the initial photoelectric conversion efficiency when the optical band gap of the second cell is set to 1.68 eV and the optical band gap value of each of the first cells shown on the horizontal axis is combined. And the deterioration rate is shown on the vertical axis.

At point P in the figure, the optical band gap of the first cell is 1.68 eV, and the optical band gap of the first cell is equal to the optical band gap of the second cell. In the direction A from the point P, the optical band gap satisfies (first cell) <(second cell). As shown in the figure, in the region (optical band gap of the first cell) <(optical band gap of the second cell) shown in the direction A, the degradation rate is low, the initial photoelectric conversion efficiency is high, This is a preferable characteristic for a photovoltaic device. This is similarly shown in the measurement results of the other samples XX.

That is, it was found that the characteristics were excellent where the optical band gap of the i-type semiconductor of the first cell on the light incident side was smaller than the optical band gap of the i-type semiconductor of the second cell.

The lowest degradation rate and the highest initial photoelectric conversion efficiency are obtained when the optical band gap of the first cell is 1.44 to 1.52 eV and the optical band gap of the second cell is It was found to be a region of 1.70 to 1.75 eV (a region surrounded by a dotted line in the figure).

(Embodiment 3) In this embodiment, the i-type semiconductor layers 107 and 104 of the first cell and the second cell in the first embodiment are used.
Has an optical band gap of 1.48 eV (Sample No. 4)
And 1.70 eV (sample No. 15), and the thickness was changed independently to produce a stacked photovoltaic device.
The same evaluation was performed.

The evaluation results are shown in Table 5 (the evaluation results are shown in a relative ratio with the prior art being 1.0, as in Example 1).

As shown in Table 5, Sample Nos. S-2 to S-5
Thickness of the first cell 300 mm, thickness of the second cell 3000-6000 mm
In this photovoltaic device, the initial photoelectric conversion efficiency is as high as 1.0 to 1.01, and the degradation rate is as low as 0.93 to 0.97, showing good characteristics. Similarly, sample Nos. S-8 to S-11 also show good characteristics.

That is, the thickness of the first cell is 200 to
It has been found that good characteristics can be obtained in the range of 450 ° and the thickness of the second cell in the range of 3000 to 6000 °. (Embodiment 4) In this embodiment, the i-type semiconductor layers 10 of the first cell and the second cell are used.
The optical band gaps of the samples 7, 104 were fixed at 1.48 eV (sample No. 4) and 1.60 eV (sample No. 2), and the film thickness was changed independently to produce a stacked photovoltaic device. Then, the same evaluation as in Example 1 was performed.

The results of the evaluation are shown in Table 6 (the evaluation results are shown in the same manner as in Example 1 by the relative ratio with the prior art being 1.0).

As shown in Table 6, Sample Nos. S-14 to S-
The thickness of the first cell is 450 Å, and the thickness of the second cell is 1500-4500.
In the photovoltaic device of (1), the initial photoelectric conversion efficiency is as high as 1.0 to 1.01, and the deterioration rate is as low as 0.94 to 0.98, showing good characteristics. Similarly, Sample Nos. S-20 to S-23 also show good characteristics.

That is, the thickness of the first cell is 350 to 650
{Circle around (2)} It was found that good characteristics were obtained when the thickness of the second cell was in the range of 1500 to 4500 °.

As described above, according to Tables 5 and 6, the i-type semiconductor 107 and the second cell 112 of the first cell 111 on the light incident side are obtained.
It has been found that an optimum layer thickness balance of the i-type semiconductor 104 exists.

[0124]

As described above, the photovoltaic device of the present invention has at least two photovoltaic cells, and the optical band gap of the first cell on the light incident side is changed to the second cell not on the light incident side. By making the optical band gap smaller than the above, it is possible to obtain an effect of realizing a photovoltaic device that has a low deterioration rate and is stable for a long period of time while maintaining the initial photoelectric conversion efficiency at a high value.

Therefore, the solar cell for power can be made highly practical.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a layer configuration of a photovoltaic device of the present invention.

FIG. 2 is a schematic diagram showing an example of a deposited film forming apparatus by a plasma CVD method for producing a photovoltaic device of the present invention.

FIG. 3

FIG. 4 is a graph showing a relative ratio between an optical band gap of an i-type semiconductor layer 107 of a first cell 111, an initial photoelectric conversion efficiency, and a deterioration rate.

[Explanation of symbols]

 Reference Signs List 101 Support 102 Lower electrode 103, 106 n-type semiconductor layer 104, 107 i-type semiconductor layer 105, 108 p-type semiconductor layer 109 transparent electrode 110 current collecting electrode 111 first cell 112 second cell 120 photovoltaic device 130 Light 201, 216, 217, 218 Film formation chamber 202 Substrate holding cassette 203 Substrate 204 Thermocouple 205 Heater 206 Substrate transport jig 207 Gate valve 208, 209 Gas inlet tube 210 High frequency power supply 211 Matching box 212 Excitation energy generator 213 Load Lock chamber 214 Valve 215 Exhaust pump

Continuation of the front page (56) References JP-A-63-58974 (JP, A) JP-A-63-66977 (JP, A) JP-A-63-48871 (JP, A) (58) Fields studied (Int .Cl. ⁶ , DB name) H01L 31/04

Claims (4)

(57) [Claims] 1. A photovoltaic device having a plurality of photovoltaic cells stacked comprises a semi conductor layer of the photoactive, the photoactivity of the first of the photovoltaic cell on the light incident side upper semiconductive <br The optical bandgap of the body layer is higher than the first photovoltaic cell.
Rather smaller than the optical band gap of the photoactive semiconductor layer of a second of the photovoltaic cell at the bottom of Le, the first photovoltaic
The thickness of the photoactive semiconductor layer of the power cell is the second photovoltaic.
A photovoltaic device characterized by being thinner than the thickness of the photoactive semiconductor layer of the force cell . 2. Light used in the first photovoltaic cell
The optical band gap of the active semiconductor layer is 1.44 to
1.52EV, thickness is 200～450A, optical band gap of the semiconductor layer of the photoactive used for the second photovoltaic cell 1.70～1.75EV, thickness 3
The photovoltaic device according to claim 1, wherein the angle is from 000 to 6000 °. 3. The light used in the first photovoltaic cell.
The optical band gap of the active semiconductor layer is 1.44 to
1.52EV, thickness is 350～650A, optical band gap of the semiconductor layer of the photoactive used for the second photovoltaic cell 1.60～1.67EV, film thickness 1
The photovoltaic device according to claim 1, wherein the angle is 500 to 4500 °. 4. The photoactive semiconductor layer is an i-type semiconductor layer.
4. The method according to claim 1, wherein
Photovoltaic device.